1. Field of the Invention
The present invention relates to elastic wave devices in which a dielectric film is provided between a piezoelectric substrate and an interdigital transducer (IDT) electrode, and to fabrication methods thereof.
2. Description of the Related Art
In the prior art, elastic wave devices are widely used as resonators and bandpass filters. Japanese Unexamined Patent Application Publication No. 2012-169707 discloses an example of such elastic wave devices. In Japanese Unexamined Patent Application Publication No. 2012-169707, a dielectric layer is formed on a piezoelectric substrate. On the dielectric layer, a first IDT electrode and a second IDT electrode are provided. The thickness of a dielectric layer disposed between the first IDT electrode and the piezoelectric substrate differs from the thickness of a dielectric layer disposed between the second IDT electrode and the piezoelectric substrate. The electromechanical coupling coefficient is varied by changing the thickness of the dielectric layer. This makes the band width ratio of the first IDT electrode different from the band width ratio of the second IDT electrode.
In the elastic wave devices having dielectric films such as one described in Japanese Unexamined Patent Application Publication No. 2012-169707, electrostatic breakdown may sometimes occur when static electricity is accumulated. For example, static electricity may sometimes accumulate due to frictional electrification during a cleaning process after resin sealing. Typically, the IDT electrode consists of two comb electrodes that are interdigitated with each other. Thus, when static electricity is accumulated at the IDT electrode, a large potential difference is generated between one of the comb electrodes and the other comb electrode. As a result, in some cases, the IDT electrode is damaged by the electrostatic breakdown.